"When dark comet UD3 was spotted near Jupiter's orbit, its existence was largely ignored. But to individuals who knew better -- scientists like Benjamin Schwartz, manager of NASA's Center for Near-Earth Object Studies -- the threat this eight-kilometer comet posed to the survival of the human race was unthinkable. The 150-million-year reign of the dinosaurs ended when an asteroid impact generated more than a billion times the energy of an atomic bomb....

"Asteroids and comets: Every year, millions of these 'stray bullets' streak the skies, and tons of small meteorites strike our planet! Some 65 million years ago, dinosaurs were wiped off the face of the earth in what many believe was the aftermath of a massive comet collision. Could something like this happen again? Scientists believe that the impact of an asteroid only a mile wide would be globally catastrophic. Join extraordinary geologist Eugene...